DURATINET COURSE - Testing Techniques for Structures...

COURSE Testing techniques for structures inspection 29th and 30th May 2012

Investing in our common futureInvesting in our common future

MECHANICAL TECHNIQUES APPLIED IN CONCRETE

STRUCTURES

Arlindo Gonçalves

André Monteiro

(LNEC)


Investing in our common future

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ADDRESSED TECHNIQUES

• Rebound Hammer

• Pull‐Out

• Pull‐Off

DURATINET COURSE - Testing Techniques for Structures Inspection LNEC • Lisbon • Portugal • 29-30 May 2012

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REBOUND HAMMER

Originally developed by the Swiss engineer Ernst Schmidt in the 1940’s

The test is covered by EN 12504‐2 andASTM C805

Measures the surface hardness of concrete

Main applications:

•Detection of zones with poor quality concrete

•Comparative testing against a concrete with known strength

•Estimation of in situ concrete strength



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Principle:

Test result: rebound number

REBOUND HAMMER


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REBOUND HAMMER

Steps:



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REBOUND HAMMER

Types of rebound hammer:

L(0.74 Nm)

P(0.88 Nm)

N(2.21 Nm)

M(29.43 Nm)


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REBOUND HAMMER

New SilverSchmidt Hammer developed by Proceq

(does not need correction for the impact direction)



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REBOUND HAMMER

Correlation with concrete compressive strength:

Influence of the type of aggregate Influence of concrete moisture contentInfluence of carbonation

Strength level: L-low; M-medium and H-highCuring conditions: empty bullets – normal curing; filled bullets – accelerated carbonation


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Pr EN 12504‐2 – What’s new?

• The results may be used for comparative testing

• A number may also be obtained in terms of velocity differential before and after the impact

• Acceptance rules for checking the rebound hammer before and after the readings

• Other anvils may be used if they provide similar readings (the mass of the reference anvil is 16 1kg)

• The hammer may be operated within the range 0oC to 50oC (before 10oC to 35oC)



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PULL‐OUT TEST

First developments by 1930 in the URSS

Major improvements published by Kierkegaard‐Hansen in 1975, naming it by Lok‐test

The test is covered by EN 12504‐3 andASTM C900

Main application:

•Assessment of concrete compressive strength


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PULL‐OUT TEST

Principle:

Test result: pull‐out force (kN)

A small metal disc, with a rod fixed centrally on one side is installed into concrete during casting, so that the rod protrudes from the surface of the concrete. The force required to pull the disc out of the concrete is measured.



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Steps:

PULL‐OUT TEST Remove the cast-in rod and connect the loading rod


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PULL‐OUT TEST

History of development (Kierkegaard‐Hansen):



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PULL‐OUT TEST

Performing pull‐out test on existing structures (Capo‐test):


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PULL‐OUT TESTType of resistance measured:

Complex triaxial stress state changing during the test and along the failure surface

The ultimate state of failure is influenced by the shear strength of the matrix mortar that controls the displacement of the aggregates at the failure surface



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PULL‐OUT TEST

Correlation with concrete compressive strength:Obtained by several authors

(15 cm cubes)Kierkegaard-Hansen

recommendation:

Some studies have shown that for high strengths the linear relation may underestimate the compressive strength


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ESTIMATION OF IN‐SITU COMPRESSIVE STRENGTH

TEST Laboratory In‐situ

Reboundhammer

15 % 25 %

Pull‐out 6‐8 % 10‐20 %



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EN 13791 ‐ ASSESSMENT OF IN‐SITU COMPRESSIVE STRENGTH IN STRUCTURES AND PRE‐CAST CONCRETE COMPONENTS

Compressive strength estimation:

•Alternative 1: Direct correlation with cores (requires 18 cores)

•Alternative 2: Correlation based on a basic curve (requires 9 cores)


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Alternative 2 (basic curves)Rebound hammer Pull-out test



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Alternative 2 (basic curve)


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CONSERVATIVE APPROACH ?!



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PULL‐OFF TEST

Originally developed in England

The test is standardized in EN 1542

Measures the bond strength between two materials

Main applications:

• Check bond strength of repair materials (coatings, paints, vanishes and repair mortars)

• Assessment of concrete or mortar tensile strength


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Principle:

Test result: bond strength (MPa)

PULL‐OFF TEST



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Steps:

PULL‐OFF TEST


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Types of failure:

PULL‐OFF TEST

A Cohesion failure in the concrete substrate

A/B Adhesion failure between the substrate and the first layer

B Cohesion failure in the first layer

B/Y Adhesion failure between the first layer and the adhesive layer

Y Cohesion failure in the adhesive layer

Y/Z Adhesion failure between the adhesive layer and the dolly



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Effect of the coring depth on the interface stresses:

PULL‐OFF TEST


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Effect of surface treatment on the interface stresses (Zhou, J. et al. 2011):

PULL‐OFF TEST



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Obrigado


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DURATINET COURSE - Testing Techniques for Structures...

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